The present invention relates to a method of feeding electric power to a plane antenna and to a plane antenna. More particularly, the invention relates a method of feeding electric power to a plane antenna which is designed for decreasing the thickness and for facilitating the assembling, and to a plane antenna capable of transmitting and receiving vertically polarized waves and horizontally polarized waves, or levo-rotary polarized waves and dextro-rotary polarized waves.
There has heretofore been known a plane antenna using a loop-type antenna element. In the plane antenna of this kind, both ends of a square or a circular loop-like antenna element are connected to balanced line connection terminals of a balanced-to-unbalanced conversion circuit and of an impedance conversion circuit through balanced feeder lines, and unbalanced line connection terminals of the balanced-to-unbalanced conversion circuit and of the impedance conversion circuit are connected to a receiver or to a transmitter through a coaxial cable.
When a feeding point is provided on a horizontal portion of the antenna element, there is obtained a plane antenna for the horizontally polarized waves and when a feeding point is located on a vertical portion, there is obtained a plane antenna for the vertically polarized waves.
If the loop-type antenna element is provided with slide element portions, a phase difference of 90 degrees is produced between the horizontally polarized waves and the vertically polarized waves due to the reactance formed by the areas and shape of the slide element portions, whereby the linearly polarized waves are converted into circularly polarized waves, forming a plane antenna for the circularly polarized waves. When the slide elements are provided at positions of about xe2x88x9245 degrees and about +135 degrees from the power-feeding point of the antenna element as viewed from the front, there is obtained a plane antenna for levo-rotary polarized waves. When the slide elements are arranged at positions of about +45 degrees and about xe2x88x92135 degrees from the power-feeding point of the antenna element as viewed from the front, there is obtained a plane antenna for the dextro-rotary polarized waves.
Thus, the conventional plane antenna requires a balanced-to-unbalanced conversion circuit and an impedance conversion circuit, i.e., requires an increased number of parts and an increased number of assembling steps, driving up the cost. It has therefore been desired to provide a plane antenna in a small size having a decreased thickness. Besides, a single antenna is not capable of transmitting and receiving horizontally polarized waves and vertically polarized waves, or levo-rotary polarized waves and dextro-rotary polarized waves. To cope with two kinds of polarization modes of the horizontally polarized waves and vertically polarized waves, or the levo-rotary polarized waves and dextro-rotary polarized waves, there must be installed antennas of two systems occupying considerable space and requiring a cost.
Thus, there arouses a technical problem that must be solved for providing a plane antenna which is fabricated using a decreased number of parts in a small size, and which is capable of coping with the two kinds of polarization modes of the horizontally polarized waves and vertically polarized waves or the levo-rotary polarized waves and dextro-rotary polarized waves, though the antenna is used in a number of only one.
The invention was proposed in order to accomplish the above-mentioned object, and provides a method of feeding electric power to a plane antenna in which a plane antenna element is arranged in parallel with a ground plane, a feeder conductor is arranged between the plane antenna element and the ground plane, the feeder conductor being in parallel with the peripheral edges of the plane antenna element, a central conductor of a coaxial line is connected to an end of the feeder conductor, and an external conductor of the coaxial line is connected to the ground plane so that the electric power is fed from the coaxial line to the plane antenna element through the electromagnetic coupling.
The invention further provides a plane antenna in which a square or a circular plane antenna element is disposed in parallel with a ground plane, feeding points of a first feeder conductor and of a second feeder conductor are arranged being separated away by 90 degrees from the center of the plane antenna element, the first feeder conductor and the second feeder conductor are provided in parallel with the peripheral edges of the plane antenna element between the plane antenna element and the ground plane, the central conductors of coaxial lines of two systems are separately connected to the feeding points of the first feeder conductor and of the second feeder conductor, and the external conductors of the coaxial lines of the two systems are connected to the ground plane to feed electric power from the first feeder conductor or the second feeder conductor to the plane antenna element through the electromagnetic coupling so as to transmit and receive the horizontally polarized waves and the vertically polarized waves.
The invention further provides a plane antenna in which a plane antenna element of the plane antenna having the first and second feeder conductors is further provided with slide elements positioned at an equal distance from the first and second feeding points so as to transmit and receive the levo-rotary polarized waves and the dextro-rotary polarized waves.